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arXiv · 2610.30095

Modeling MAD Sgr A* flares and their dependence on spin

Eleni Antonopoulou·Antonios Nathanail·Yosuke Mizuno·Foivos Zanias
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Abstract

Aims: This study aims to place constraints on the spin of Sgr A* from recent flare observations. It models the flare kinematics in the vicinity of a supermassive black hole, evaluates their dependence on black hole spin, and assesses the correlation between the spin of the black hole and the astrometric observations in the Galactic center. Methods: Our study extends the work of Antonopoulou et al. 2025 to a range of black hole spins. A prominent flux eruption is identified in the simulation, and the evolution of the active region on the equatorial plane is tracked during the event. The flare model consists of a spherical hot spot ejected along the flux tube with a relativistic velocity. Results: In MAD simulations, the flux tube wraps around the jet funnel in the opposite direction to the black hole's spin. This dependence is imprinted on the flare trajectory and provides a strong correlation between the spin of the black and the flare kinematics. This analysis favors Kerr black holes, with a preference towards larger spin magnitude. Although prograde simulations show a consistent clockwise motion in the sky regardless of disk rotation, retrograde models require a clockwise accretion disk to account for the observations of July 22, 2018. Conclusions: A maximally rotating Kerr black hole is the most promising candidate for reproducing the observed flare trajectory in the vicinity of Sgr A*, illustrating a pass faction surpassing $90\%$ among the investigated flare models. In particular, determining spin orientation within this model is linked to the rotation of the accretion disk. Assuming a counterclockwise accretion disk, a prograde black hole with $a\geq1/2$ is able to reproduce the observed flare kinematics in the Galactic center. Conversely, assuming a clockwise rotation for the disk, the observations support both prograde and retrograde Kerr black holes with a large spin.

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Eleni Antonopoulou, Antonios Nathanail, Yosuke Mizuno, Foivos Zanias. 2026-10-21. Modeling MAD Sgr A* flares and their dependence on spin. https://arxiv.org/abs/2610.30095

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